When I returned from my trip to Vietnam a couple of summers ago, I brought back a very intriguing souvenir. It was an old coin that dated back to 1908 and was purportedly about 27 grams of 90% pure silver. Now, I assumed that the coin was a fake. I got the coin from a shop that was no bigger than my closet, sandwiched between two other shops. Nevertheless, I adored this coin as it was a very cool fake. I joked with my dad about how it would be interesting if it were real silver. Surprisingly, later that summer, I discovered that the coin was probably real silver by using some tests based on the interesting properties of silver.
The Magnet Test
Silver has many different kinds of properties that can differentiate it from other metals and alloys (mixtures of metals). When I saw these coins, I immediately took out my magnet and went to check if it could attract the coins. There are actually 6 different types of magnetism. What most people just call magnetism is actually called ferromagnetism. Many commonly used metals are ferromagnetic, such as iron, steel, and nickel. Silver is not ferromagnetic meaning that it is not attracted to other ferromagnets. In my case, the magnet did nothing meaningful to the coin so it passed the first test. While this helps to eliminate lots of easy fakes, it still could be made out of non-magnetic metals or alloys, like zinc, copper, aluminum, and so on. Therefore, I had to do a couple more tests.
The Sound Test
Another test that I had unwittingly conducted was the Ping Test, Noise Test, or Sound Test. It is possible to use the sound of the coin being hit, to determine whether or not it is made of silver. It should be like the reverberation of a bell. Many other metals sound dull when it, not holding the sound or making a clear tone. Silver, on the other hand, makes a loud and satisfying ping. This was largely evident when I flicked the coin for fun. In comparison, an old Canadian dollar coin, about the size of a toonie, does not ring out when flicked. The old Canadian dollar has a composition of about 99% nickel. This test might sound rather unintuitive, but if you’ve ever heard the stock coin flip sound, then you likely know what silver sounds like when hit.
The Magnet Slide
The final test that I conducted was at a summer camp that had a lot of neodymium magnets. By laying them out in a long strip and placing them at a slant, I was able to make what is called a magnet slide. The Magnet Slide test checks for a property that is actually present in every material; Diamagnetism. One of the 6 magnetic forces, Diamagnetism is a complex quantum effect that every material possesses. In day to day life, it goes unnoticed because of how tremendously weak it is in comparison to other forces. That’s why even though all materials have diamagnetic properties most materials are still considered “non-magnetic”. However, some materials can be notably more affected by diamagnetism such as gold, copper, and luckily for me, silver.
By placing the coin at the top of the magnet slide and letting it down, it will move down significantly slower than other, less diamagnetic metals such as aluminum or zinc. When a material is introduced to a magnetic field, it will generate a repulsive force. This repulsion slows down the coin to a noticeable degree. At this point, there was enough evidence to satisfy me.
The Properties of Elements
There are many different kinds of elements that all have unique properties. Understanding the special properties of elements make it easier to sort, compare, and use them in different capacities. It might seem pointless to learn about forces like diamagnetism due to its weak nature, but try hard enough and you can essentially invent a levitation machine.
TL;DR – Buy cool coins, you might get some real silver, and learn about quantum physics at the same time.